Electronic data is continuously being generated and stored in some kind of medium. Stored data can be exposed to a full spectrum of different access patterns, which in many cases are dependent on data type. Some types of data have a short life or persistency, or require to be accessed quickly. Other types of data may have a period of frequent access in their early stages, but become less needed over time. As data “ages” it usually becomes accessed less frequently. Some data may eventually get purged, while others may get archived for long-term storage.
Data storage and access patterns are also based on cost. To handle the various types of accesses to data in their respective lifecycle in a cost effective manner, a plethora of storage devices are used. Many of these storage devices use some kind of storage disk, referred to as a “hard disk,” which is a disk of plastic or metal material having an electromagnetically charged surface or set of surfaces on which large amounts of data can be stored and read from. Data having continuous access patterns and requiring fast bandwidth will most likely reside in fast-access disks, such as fast Small Computer Systems Interface (SCSI) disks or disk arrays. Data needing to be accessed much less frequently may reside in slower-access disks, such as Serial Advanced Technology Attachment (SATA) disk arrays. Data for long-term archival is usually stored on serialized tape. Data requiring portability is typically stored in removable media such as Compact Disk-Read Only Memory (CD-ROM), Digital Video Disk (DVD) ROMs, removable hard disk platters, and portable hard drives.
Migrating data to a lower performance but lower cost storage medium is primarily based on the relative “value” of that data, i.e. a price that can be associated with the data based on its economic, social, or functional importance or desirability, and as compared with all other similar or similarly available data. As the value of the data decreases, storage costs can be decreased by having less-valued data hosted on less costly storage media. Even if the value of data does not decrease over time, the amount of data generated over time can be burdensome, thus also requiring a lower cost storage medium.
Each specific type of storage device has advantages and disadvantages. Most storage devices that employ hard disks (or simply called “disks”), such as a Redundant Array of Independent Disks (RAID) device or other type of disk “pool,” provide high data reliability, fast random access to data, high data throughput, and very low latency. Disks are typically of rugged construction and can tolerate diverse environments. However, disks have a number of disadvantages, among which is a limited life governed by the operating environment of such factors as heat, vibration, disk activity such as power-on hours, and the number of spin ups. Disks are also relatively expensive compared to other media, generate significant heat, and consume a relatively large amount of power.
Disks are always kept spinning, or “spun up,” to ensure quick access to data. Thus, disks are typically active while the associated access system is active. Some access systems will spin a disk up if the data on the disk is accessed, and use an inactivity timeout to spin the disk down. As a result, the operational state of a disk is directly affected by the access pattern or activity of its content. In other words, any given disk may only be as active as the access pattern of the most-accessed data stored on it. Thus, a disk that contains a unit of data that is continuously accessed cannot be spun down.
Tapes are inexpensive but can hold very large amounts of data for long periods of time. However, data stored on tapes can only be accessed in a sequential manner, resulting in very slow access speeds and high latency. CD-ROMs and DVDs are very inexpensive but can only hold limited data. They also are known to have short data retention periods if the quality of the disks is poor. Most CD/DVD disks are write-once, or allow only limited write cycles. Portable media, like CD-ROMs, DVDs, and removable hard disks, require significant manual intervention to secure data, identify content, and integrate to and from enterprise storage systems.
What is needed is a storage device having the properties of high speed, high reliability, low cost, low heat generation, low power consumption, and long-term data archiving.